Log Message:
py-pip: update to 20.3.4.

20.3.4 (2021-01-23)
===================

Features
--------

- ``pip wheel`` now verifies the built wheel contains valid metadata, and can be
  installed by a subsequent ``pip install``. This can be disabled with
  ``--no-verify``. (`#9206 <https://github.com/pypa/pip/issues/9206>`_)
- Improve presentation of XMLRPC errors in pip search. (`#9315 \ 
<https://github.com/pypa/pip/issues/9315>`_)

Bug Fixes
---------

- Fixed hanging VCS subprocess calls when the VCS outputs a large amount of data
  on stderr. Restored logging of VCS errors that was inadvertently removed in pip
  20.2. (`#8876 <https://github.com/pypa/pip/issues/8876>`_)
- Fix error when an existing incompatibility is unable to be applied to a \ 
backtracked state. (`#9180 <https://github.com/pypa/pip/issues/9180>`_)
- New resolver: Discard a faulty distribution, instead of quitting outright.
  This implementation is taken from 20.2.2, with a fix that always makes the
  resolver iterate through candidates from indexes lazily, to avoid downloading
  candidates we do not need. (`#9203 \ 
<https://github.com/pypa/pip/issues/9203>`_)
- New resolver: Discard a source distribution if it fails to generate metadata,
  instead of quitting outright. This implementation is taken from 20.2.2, with a
  fix that always makes the resolver iterate through candidates from indexes
  lazily, to avoid downloading candidates we do not need. (`#9246 \ 
<https://github.com/pypa/pip/issues/9246>`_)

Vendored Libraries
------------------

- Upgrade resolvelib to 0.5.4.